Known turbochargers are used for power augmentation of reciprocating piston engines. So that the turbine can be operated as efficiently as possible, the exhaust gas is deflected in front of the turbine in a row of guide vanes of a guide vane device, also called a nozzle ring. In exhaust gas turbochargers with radial turbines, the nozzle ring includes (e.g., comprises) two fastening rings, which delimit the flow passage on both sides, and a plurality of guide vanes, which, depending upon application, are at a specified angle in relation to the flow and also have a different length.
FIG. 13 shows a schematic sectional view of a known exhaust gas turbocharger with radial turbine having a nozzle ring on the turbine side in accordance with the state of the art. As shown in FIG. 13, the exhaust gas turbocharger has a radial-inflow exhaust gas turbine and a radial compressor 2. So that the exhaust gas turbine can be operated as efficiently as possible, the exhaust gas, before reaching the turbine wheel 3, is directed in a guide vane device, this being the nozzle ring 1, onto the rotor blades 31 of the turbine wheel 3.
If the nozzle ring 1 is produced in one piece by means of sand or investment casting processes, the flow guiding is as a rule certainly very good, for which a separate casting pattern has to be manufactured for each blade angular position. Moreover, the flexibility for additional angular positions or guide vane spacing's is limited since with each change a new casting pattern has to be produced, which both becomes expensive and results in a very long lead time.
In addition, there is a known method in which guide vanes are welded or soldered in individual rings. In this method, the flow guiding is optimum, but new rings should be provided for each angular position, for which the costs are a little less than in the case of the investment casting process.
In the most cost effective production variants of those which are widely applied, plates are welded or soldered between the fastening rings instead of prismatic profiles. The formed guide vanes are arranged in recesses in the fastening rings and welded or soldered therein. In the case of such nozzle rings, the flow guiding is considerably poorer than in the case of the two first-named variants on account of the plate profiles. Moreover, the walls are extremely thin in such nozzle rings and therefore susceptible to erosion as a result of exhaust gas particles.
Therefore, when nozzle rings are being produced a compromise between costs and efficiency of the nozzle ring should be adopted. To date, there has been no production method which is noticeably more cost effective than the investment casting process and still achieves a comparable, excellent flow guiding.
One known solution involves the assembly of nozzle rings from two fastening rings and from a multiplicity (e.g., plurality) of vanes of identical construction, as a result of which flexibility in production is significantly improved. So that assembled nozzle rings can cover the main functions of vane position and vane length (spacing's of the two fastening rings), but also include additional functions such as fastening of the entire nozzle ring in the turbocharger or sealing against leakage flow, different, or at least differently finished, base components are often used.